for those with 48volt systems

[Lloyd]

who is selling the balmar mc48?

bob g

balamr,

If ya need a part # let me know,  I just had em build me 2 X's MC32v regs based on the same, they can do 24,32,36, & 48 native from the same reg/w software changes.

Lloyd

[bentcrafter]

balamr,

If ya need a part # let me know,  I just had em build me 2 X's MC32v regs based on the same, they can do 24,32,36, & 48 native from the same reg/w software changes.

Lloyd

Regs I got.... so where are the 'efficient' high amp rectifiers? In 2 months keyboarding, I unearthed only one that I could actually buy, and it's only a 50 amp. Just yesterday, I put in an order for two GMM3x120-0075X2-SMD modules the vendor advertised as "in stock". Not 2 hours later, I received the following;

"Im sorry, but we don't have this parts available at stock or with any short lead time now, seems like it's a rare thing at our market. please feel free to contact me on any questions. Maybe you need something else to quote?"

[mobile_bob]

not sure why the interest in a high efficiency rectifier?

at 48volts nominal, the voltage drop comprises about 1/4 the loss of a 12 volt nominal system, as it relates to the diodes.

its very unlikely that you will find a high efficiency rectifier that will reduce this to half of that, or 1/8th that of a 12volt system.

you rapidly reach the point of diminished returns.

i think you will find your choice of alternator will have a much larger impact on the overall efficiency of the system, just as your choice of prime mover.

another consideration is cost and reliability
a high efficiency rectifier is likely to be priced substantially higher than the replacement diodes i listed earlier, and i would also be concerned with reliability.

diodes can and will fail,

i would be very concerned with the "load dump" capability of any rectifier i planned on using.

just a thought?

what are you goals?

bob g

[bentcrafter]

not sure why the interest in a high efficiency rectifier?

[mobile_bob]

how about a little more data

what alternator does the chart relate to?

what operating voltage nominal and at load?


also not the increase in efficiency between the first column and the second
column..

the third column really does not illustrate the change in rectifier alone, it also takes
into account the replacement of the field with neo magnets and the reduction of stator resistance, both of which are the factors responsible for the increase in efficiency.

so naturally i want to see more info so i can get my head wrapped around this one.

also in the first column the rectifier loss is about 100 watts more than the mosfet
rectifier of the second column. shaving that 100watts off the rectifier by going to a mosfet while useful is probably going to be a costly cut in losses.

what i mean is this, that 100watts comprises 1/4 of the efficiency effect at 48volts as it would at 12 volts

for instance a 12 volt @100amp alternator with a 100 watt diode loss would work out to be 12 x 100=1200watts -100 watts = 1100 watts  or 1100/1200= 91.6% or an effective loss 8.4% attributed to the diodes

on the other hand 48volt@100 amps with the same 100watt diode loss would work out to be 48 x 100 = 4800watts - 100 watts = 4700watts or 4700/4800= 97.9% or an effective loss of just 2.1%

of course the number shift a bit due to actual charging voltages, but you get the idea.

don't get me wrong i am all about finding even fractions of a percent in efficiency gains, so long as the price is not prohibitive and there are no reliability issues.

so in recap
what alternator is the chart related to?
what voltage are they working at?  and at load?

thanks
bob g

[mobile_bob]

it would appear the alternator in question is a 12volt nominal unit
probably tested at about 14.6-14.8vdc at load

bob g

[BruceM]

I would think that switching to Schotky diodes for a 12V alternator could reduce the loss by at least half.  Less robust, but so is synchronous rectification.  So even at 12V what you are looking at is largely marketing hype.

As mobile_bob point out the losses shown are for 12V, and are bogus for 48V.  But the losses do point out the inherent inefficiency of low voltage systems.  In most power electronics designs, you rarely see synchronous rectification used except for 6 volts and below, because with schotky diodes, it just isn't worth the complexity until you get that low.

The integrated rectifier/charge regulator Brentcraft found seems a good choice, since there is no reliability penalty for the low side Mosfets; they are both regulating and providing "half synchronous" rectification by eliminating the low side diodes. But at 40 amps it alas isn't rated high enough current for many 48V charging apps.

Of course, I say why stop at 48V, Edison had it right at 120VDC as a good compromise for safety and being able to run power about without using tons of copper. At 120VDC, your diode loss should be significantly less than 1/10th, as diode bridge voltage drop is reduced at the lower currents. 

[mobile_bob]

Bentcrafter

that chart has been haunting me, somewhere in the back of my mind
i couldn't get past the idea that i had seen it somewhere before.

been laid up with the flu for 4 days now, and it finally popped back into my head

i have seen this chart somewhere before, but can't remember where!



bob g